U.S. Pat. Nos. 3,299,500 and 3,314,138, disclose self-piercing female elements, including nuts, which may be simultaneously clinched to secure the nut in a panel opening. Additionally, U.S. Pat. Nos. 3,938,239 and 4,018,257 disclose self-riveting nuts, including nuts having an annular skirt or barrel portion wherein the free end of the barrel portion is deformed radially outwardly in a die member to form a mechanical interlock with a panel. However, the self-riveting nuts disclosed in the above referenced patents are secured to the panel having a pre-pierced panel opening. This has the disadvantage of requiring two separate operations, the first operation involves creating the panel opening, and a second operation involves installing the female fastener. Additionally, such methods also require very precise centering of the nut relative to the pre-pierced panel opening, wherein a spring biased pin is received through the panel opening and the nut is centered on the pin prior to installation. U.S. Pat. No. 3,926,236 discloses a method of attaching a nut to a panel wherein the panel is pierced by a punch which extends through the nut bore to pierce and secure the nut to a panel in continuous operation, however, the fastener is not a riveting-type fastener which has a barrel portion extending through the pierced panel opening.
U.S. Pat. No. 3,800,401 discloses methods of attaching closures to a container such as a tag ring in a continuous operation. This application and the above-referenced related patents and applications disclose methods and apparatus for attaching male and female elements to a panel in a continuous operation. The preferred methods of installation do not require pre-piercing of the panel, although the fastener is equally suited for installing in a pre-pierced panel opening.
U.S. Pat. Nos. 4,193,333 and 3,871,264 disclose means of attaching a stud-like fastener, wherein the stud includes an annular end portion which penetrates a plate or structural steel member, which may be deformed radially around a plug pierced from the panel.
U.S. Pat. Nos. 1,976,019; 2,456,118; 2,521,505; 3,436,803; 3,754,731; 4,039,099; and 4,092,773 disclose various riveting techniques, wherein the fastener includes an annular end portion which may be press-fitted through an opening in a panel. The annular end portion is then riveted or radially outwardly deformed by a die member having an annular semi-toroidal die cavity and may include a projecting central die portion which is received in the annular riveting end of the fastener.
Although the above-referenced patents do disclose self-riveting male and female fasteners, and methods of installing same, they do not disclose a riveting stud type fastener which is suited for making a reliable electrical grounding connection to a metal panel or the like. For example, U.S. Pat. Nos. 4,193,333 and 3,871,264 which disclose methods of attaching stud fasteners to a panel, primarily teach a methodology for providing superior mechanical interlock between the stud fastener and the panel and do not address the issue of the electrical integrity of the connection. It is well known that a fastener can provide excellent mechanical bonding to a panel while providing unacceptable electrical conductivity to the same panel. For example, various coatings could be present on an electrically conductive panel which, although not interfering with the mechanical interlock between the stud fastener and the panel, may partially, or entirely impede the flow of electrical current through the fastener and panel interface.
Accordingly, it is the primary object of this invention to provide a stud type fastener which is adapted to be attached to an electrically conductive panel wherein the fastener provides both superior mechanical connection to the panel while also providing excellent electrical conductivity across the fastener/panel interface. Further, the fastener and method herein disclosed are particularly suited for mass production applications, particularly automotive applications utilizing automatic presses. The fastener of the present invention can be used in a panel having a pre-pierced opening, but is not limited to free pierced applications inasmuch as the present fastener is adapted to pierce the panel during the installation process.